Abstract: Phylogenetic reconstructions of diverse tropical groups have yielded biological insights that extend well beyond the field of systematics, illuminating such topics as biome assembly and plant–insect coevolution. In this issue of New Phytologist, De-Nova et al. (pp. 276–287) present a rigorous time-calibrated phylogeny of the Neotropical tree genus Bursera in order to estimate lineage ages, and to investigate how geography and ecology have structured its species diversification. Because Bursera is a dominant component of Mesoamerican seasonally dry tropical forests (SDTFs), the study provides evidence relating to the origin and expansion of this important biome. The study also sets the record straight on the age of a well-known plant– herbivore interaction.